Thrombosis as well as atherosclerosis may result from injury to the endothelial cells (EC) lining the artery wall. One hypothesis to explain removal or death of EC which might trigger vascular disease, is that the shear stress of the flowing blood, or changing shear stress resulting from pulsatile patterns of flow, damages the EC. There is indirect evidence to support this hypothesis from in vivo studies and isolated vessel studies. However, the present proposal will provide direct evidence for the effect of shear stress on tissue cultured bovine EC. To accomplish this, pure EC cultures will be subjected to defined levels of shear stress in a closed in vitro circulatory loop with essentially steady, laminar, Poisueille flow conditions. Cell responses in steady flow will be compared to those in a pulsatile flow loop designed to simulate flow and pressure characteristics in the descending thoracic aorta. The substrates for cell culture will be tubes of clinically relevant biomaterials in porous and nonporous configurations of polyether urethane and Dacron velour. Cell proliferation, basement membrane collagen synthesis, permeability, and morphological change in response to flow conditions will be studied. Methods for assessing these properties will be H3 thymidine uptake as a reflection of cell proliferation; H3 proline incorporation into collagen as a measure of basement membrane synthesis, penetration of horseradish peroxidase across the endothelial barrier as a measure of permeability, and light, scanning electron, and transmission electron microscopy. Tissue culture of pure EC has led to elucidation of EC functions in stationary culture. However the goal of this proposal is to define the effects of physical forces exerted by the blood on EC function.